On the mechanism of proton translocation

Of the four redox centres, haem a is the most likely one to be coupled to proton translocation (Fig. 3.6). It exhibits heterogeneous oxidoreduction kinetics, membrane sidedness with respect to proton dependence, and looses the proton-dependence of oxidoreduction simultaneously with loss of proton pumping when subunit III is removed from the enzyme (see below, and discussion in Refs. 92, 99). 

However, the details of the molecular mechanism of redox-linked proton translocation are still largely unknown, not only for cytochrome oxidase but for the entire respiratory chain. In considering various possibilities it is important to distinguish between basically different elementary steps of the process. Proton conduction through the protein is but one such element. Several possible mechanisms have been proposed for this function, based on conduction along hydrogen-bonded networks of amino acid residues within the membrane (reviewed in Ref. 8). In redox-linked 

The most intriguing question regarding molecular mechanism concerns the nature of the molecular linkage between the acidic group and the redox centre. In cytochrome oxidase the formyl carbonyl and the propionate carboxyls of haem a have specific properties that make them potential candidates for providing such a linkage [92,99,167-169]. 

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